KH Over Oiling - a different question

[SteveHands]

No Paul, the one-way valve in the breather hasn't solved the issue, but it has reduced it a bit.

Since my last posting I have modified the rocker oil feed so that it's now tee'd off the return to the tank. I put a small restriction in the tank side of the T-Piece to ensure flow to the rockers. I've done about 170 miles with that setup and the rockers haven't seized so I guess that's working. That also didn't reduce the smokiness.

I'm now wondering if I'm getting oil pooling in the left side crankcase. Some long time ago the left case was damaged, possibly by a broken rod punching through or maybe an accident. Wasn't obvious at first because the repair is so good, but I finally noticed it when I realised why it had a gasket between the halves - because the case had been re-faced following repair, and the gasket it there to correct the spacing.

I'm thinking that if the internal shape of the case is now distorted and retaining a pool of oil, that could be picked up by the flywheel and thrown up the bore. Or maybe the clearance between flywheel and case is now too small which could cause the same thing. I know it's fairly close anyway. I also know that many wet-sump machines have a baffle plate in the sump to prevent oil surge being picked up by the crank.

Final thing - I'm going to try running without the mesh box around the pump. It's been suggested that the ultra-fine mesh is restricting oil flow to the return side of the pump. I have had a similar thing in a race bike where the pattern-part filter mesh on the oil tank pickup was so fine that once the oil was aerated by the return churn it would just suck the air bubbles through and not the oil and destroy the crank. Took three cranks to spot that one and the problem went away when I cut the mesh off. Thoughts?

[Paul Slootheer]

Sorry to hear you are still struggling with the oil problem. I guess you allready know KH pumps are notorious for wet sumping? The pump on its own looks to work ok, so this can not be the problem. You also altered oil flow upstairs. What more can you do? I can’t imagine distortion of the cases will create this specific problem. I know it’s a lot of work, but did you checked the piston rings for the gaps/damage?

[nevhunter]

The scavenge Pump should have about 2 times the capacity of the supply one. That should ensure that Bubbles are returned soon after starting the Motor. The ARIEL 500 twin has a fairly high rate of Oil flow which is very evident with the filler lid OFF. It's a special OIL tank. Nev

[paul.jameson]

Having read through this topic again it seems to me that the problem is most likely to be oil going down the valve guides. I note that you have replaced the tappet guides with the Club ones which have extra grooves to increase the oil draining. But did you carry out the modification to the cylinder before fitting them? This modification is listed in the Ariel Service Bulletins as No 127A but the associated drawing is not in the Service Bulletins file and hence not on the website. I confess that it took me quite a while to track it down but please find it attached, complete with Service Bulletin 127A.

[nevhunter]

It's really a (Factory) Mod to do. Retro for ALL 500 cc models. I wonder who would" set up" to do that? Good info Paul. Nev

[SteveHands]

Ah. No Paul, I didn't know about the factory mod but I shall investigate whether I can do it. Thanks for the drawing.

Latest update:
It wasn't the filter gauze - was clutching at straws there anyway.
I have stripped the top end and have found a couple of things:

1. The piston rings are intact.
2. There is definitely oil coming down the exhaust guides. Not so much the inlets since I've added seals to those. I'll send a drawing of the mod and seal number to Cheval since it might be useful to others.
3. With the head off there is significant 'breathing' up the pushrod tube holes when turning the engine, which disappeared when I removed the dynamo for barrel nut access.

So I think it is a breathing problem. The new tappet guides are allowing more pressurisation of the rocker boxes which is shoving the, theoretically, reduced rocker oil supply down the clearance in the guides. I say theoretically because I did note that when running with the rocker covers off there is significant oil being blown back up the pushrod tubes.

I've bought new exhaust valves and guides but I don't think that will completely fix the issue since the crankcase breather is very low capacity compared to most other British twins I've worked on. By comparison, the exhaust valves & guides in my 6T are just as worn but that's not smoky at all, but it does have decent crank breathing and additional breathers on rocker boxes and chaincase (ex drag-race bike).

Once reassembled I will run with the dynamo off and on for exhaust smokiness comparison. If dynamo-off does reduce smokiness I'll have to think about modding the original breather or adding one somewhere. I think I'm on the right track because when I added a one-way valve to the original breather pipe the smoking did reduce a little.

I think you're right about it not being crank clearance Nev - more straw-clutching there I'm afraid - and I have noted how quickly the crankcases refill with oil, drained on Monday, an inch of oil in them Friday night. I'm wondering if there's space in the bottom of the rocker feed drilling for the type of non-return valve in B31s etc.....